The term medical tomography apparatus encompasses, for example, computed tomography (CT) scanners, magnetic resonance (MR) tomography scanners, angiography scanners, single proton emission computed tomography (SPECT) scanners and positron emission tomography (PET) scanners.
In planning the acquisition of tomographic images by means of a medical tomography apparatus, use is often made of topograms. As a preliminary step in a CT imaging session, a topogram scan is performed in such a way that the topogram, i.e. the overview image, is recorded at a specific angle (for example, anterior-posterior or lateral) with a stationary X-ray source and stationary detector arrangement and—compared to the subsequent actual CT scan which leads to the acquisition of images suitable for diagnostic findings—at a lower radiation dose. The positioning of the examination object, i.e. the patient, for example, on the patient table of the tomography apparatus is carried out in this case such that the examination object is placed onto the patient table.
In order to indicate the start position of the topogram scan (and/or of the ensuing imaging scan) for the user (i.e. the radiologist or radiological technician), a marking can be made by means of a laser marker integrated into the tomography apparatus. Such a solution is disclosed for example in the German patent application DE 10 2011 004 747 A1. A fixed length of the topogram scan can be set on the operator console of the tomography apparatus and the scan can be performed. Optionally, the topogram scan can be terminated prematurely by pressing a stop button in order to reduce the radiation dose to a minimum.
The problem resulting from this method of proceeding is that only the start position of the (topogram) scan is visualized by way of the laser marking in the region of the patient table, but not the end position of the acquisition field of view. Even if a further marking laser were to be available, a further problem would exist in that the setting of the acquisition field of view is carried out only from the control room, since the options for operator control of the tomography system in the actual examination room are very limited. As a consequence the end position of the topogram can only be set by the user's moving back and forth several times from the examination room to the control room, which significantly complicates the clinical workflow. Furthermore, the laser marking is carried out in the examination region of the tomography apparatus, i.e. inside the so-called gantry, in other words at the place where the images are subsequently acquired: This is because that is where the marking laser is located. This necessitates moving the examination object into the gantry, thereby greatly restricting the user's field of vision at the same time, which makes it considerably more difficult to achieve an optimal setting of the acquisition field of view.
The article by Martin Sedlmair titled “Nadelpositionierung and Steuerung” (“Needle positioning and control”) in the journal Technik Up2date 2010 No. 9, pp. 60 to 61, proposes using an LCD video projector for projecting anatomies onto a patient on a patient table of a tomography system. However, this solution is associated with a relatively high level of technical complexity and financial outlay, and in addition, due to the typically relatively low light output of LCD video projectors, is only suitable to a limited degree for displaying an acquisition field of view. If, on the other hand, a high light output is set, there is the risk of dazzling the patient and/or user, so that protective glasses for user and patient might even have to be used, which overall entails a negative intrusion into the clinical workflow.